Doppler system for measurement of blood flow during cardiopulmonary bypass and ventricular assist

摘要

An ultrasonic Doppler flow measurement system for measuring blood flow in a polymer conduit includes an ultrasonic transmitter transducer, an ultrasonic receiver transducer, an amplifier/detector circuit for producing a Doppler signal which varies in frequency as a function of blood velocity, a clipping circuit, an automatic gain control circuit, and a frequency-to-voltage converter which produces an output signal having a voltage which is a function of flow velocity. The automatic gain control circuit accomodates variations in Doppler signal strength due to varying red blood cell concentration. The clipping circuit prevents an inordinate reduction of gain by the automatic gain control circuit due to extremely large, occasional gas bubbles or fat globules in the blood.